Ion‐beam mixing at an Fe:metallic glass (Fe67Co18B14Si1) interface is studied by employing the technique of conversion electron Mo¨ssbauer spectroscopy (CEMS). A 230‐A˚‐thick overlayer of iron (enriched to 33% in the concentration of57Fe Mo¨ssbauer isotope) was deposited on the shiny surface of metallic glass and such composites were bombarded with 100‐keV Kr+ions at dose values in the range between 1×1015and 2×1016ions/cm2. The transformations in the local atomic arrangements across the interface were investigated by monitoring the changes in the hyperfine‐interaction parameters. It is shown that mixing leads to significant changes in the composition, in the vicinity of the interface as a function of the ion dose. At low dose (1×1015ions/cm2) the local atomic coordination is found to be rich in the transition‐metal concentration, while at a higher dose (2×1016ions/cm2) it is observed to be rich in the boron concentration. Interestingly, at an intermediate dose 1×1016ions/cm2the composite near the interface region partially crystallizes and this structural state is found to revert back to the amorphous state upon thermal annealing at 300 °C. The observations made on the basis of CEMS are well supported by x‐ray diffraction measurements.